If you aren't moving at a snail's pace, you aren't moving at all. -Iris Murdoch

Monday, November 28, 2005

Pleistocene snails: Vallonia gracilicosta

I have tentatively identified this little charmer as Vallonia gracilicosta. A rather small snail, it is common to the Rocky Mountain regions, however, a few scattered populations exist east of the Mississippi (see map below). Scale ticks in photos are in mm.

Map of the distribution of fossil (tan) and living (blue) V. gracilicosta. The range for this species shifted from the Midwest to the Rockies after the retreat of the Laurentide Ice sheet 10,000 years ago. It is also possible that previous to the Pleistocene, V. gracilicosta inhabited the Rocky Mountain region, invading the midwest during the last glacial maximum. Map is from the US Census website, while biogeographic data comes from: Pilsbry, 1939; Nekola et al., 1999; Nekola, 2002; Frest and Dickson, 1986; Hubrict, 1985; Baker et al., 1986.